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</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><ul><li><code>set_timer</code> 可以创建一个 <strong>事件</strong></li> <li>可以在 <strong>游戏循环</strong> 的 <strong>事件监听</strong> 方法中捕获到该事件</li> <li>第 1 个参数 <strong>事件代号</strong> 需要基于常量 <code>pygame.USEREVENT</code> 来指定
<ul><li><code>USEREVENT</code> 是一个整数，再增加的事件可以使用 <code>USEREVENT + 1</code> 指定，依次类推...</li></ul></li> <li>第 2 个参数是 <strong>事件触发</strong> 间隔的 <strong>毫秒值</strong></li></ul> <p><strong>定时器事件的监听</strong></p> <ul><li>通过 <code>pygame.event.get()</code> 可以获取当前时刻所有的 <strong>事件列表</strong></li> <li><strong>遍历列表</strong> 并且判断 <code>event.type</code> 是否等于 <code>eventid</code>，如果相等，表示 <strong>定时器事件</strong> 发生</li></ul> <h3 id="_1-2-定义并监听创建敌机的定时器事件"><a href="#_1-2-定义并监听创建敌机的定时器事件" class="header-anchor">#</a> 1.2 定义并监听创建敌机的定时器事件</h3> <p><code>pygame</code> 的 <strong>定时器</strong> 使用套路非常固定：</p> <ol><li>定义 <strong>定时器常量</strong> —— <code>eventid</code></li> <li>在 <strong>初始化方法</strong> 中，调用 <code>set_timer</code> 方法 <strong>设置定时器事件</strong></li> <li>在 <strong>游戏循环</strong> 中，<strong>监听定时器事件</strong></li></ol> <h4 id="_1-定义事件"><a href="#_1-定义事件" class="header-anchor">#</a> 1) 定义事件</h4> <ul><li>在 <code>plane_sprites.py</code> 的顶部定义 <strong>事件常量</strong></li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 敌机的定时器事件常量</span>
CREATE_ENEMY_EVENT <span class="token operator">=</span> pygame<span class="token punctuation">.</span>USEREVENT
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><ul><li>在 <code>PlaneGame</code> 的 <strong>初始化方法</strong> 中 <strong>创建用户事件</strong></li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 4. 设置定时器事件 - 每秒创建一架敌机</span>
pygame<span class="token punctuation">.</span>time<span class="token punctuation">.</span>set_timer<span class="token punctuation">(</span>CREATE_ENEMY_EVENT<span class="token punctuation">,</span> <span class="token number">1000</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h4 id="_2-监听定时器事件"><a href="#_2-监听定时器事件" class="header-anchor">#</a> 2) 监听定时器事件</h4> <ul><li>在 <code>__event_handler</code> 方法中增加以下代码：</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">def</span> <span class="token function">__event_handler</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    
    <span class="token keyword">for</span> event <span class="token keyword">in</span> pygame<span class="token punctuation">.</span>event<span class="token punctuation">.</span>get<span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>
    
        <span class="token comment"># 判断是否退出游戏</span>
        <span class="token keyword">if</span> event<span class="token punctuation">.</span><span class="token builtin">type</span> <span class="token operator">==</span> pygame<span class="token punctuation">.</span>QUIT<span class="token punctuation">:</span>
            PlaneGame<span class="token punctuation">.</span>__game_over<span class="token punctuation">(</span><span class="token punctuation">)</span>
        <span class="token keyword">elif</span> event<span class="token punctuation">.</span><span class="token builtin">type</span> <span class="token operator">==</span> CREATE_ENEMY_EVENT<span class="token punctuation">:</span>
            <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;敌机出场...&quot;</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><h2 id="_02-设计-enemy-类"><a href="#_02-设计-enemy-类" class="header-anchor">#</a> 02. 设计 <code>Enemy</code> 类</h2> <ol><li>游戏启动后，<strong>每隔 1 秒</strong> 会 <strong>出现一架敌机</strong></li> <li>每架敌机 <strong>向屏幕下方飞行</strong>，飞行 <strong>速度各不相同</strong></li> <li>每架敌机出现的 <strong>水平位置</strong> 也不尽相同</li> <li>当敌机 <strong>从屏幕下方飞出</strong>，不会再飞回到屏幕中</li></ol> <p><img src="media/15025309517247/014_%E6%B4%BE%E7%94%9FEnemy%E5%AD%90%E7%B1%BB.png" alt="014_派生Enemy子类-w657"></p> <ul><li><strong>初始化方法</strong> <ul><li>指定 <strong>敌机图片</strong></li> <li><strong>随机</strong> 敌机的 <strong>初始位置</strong> 和 <strong>初始速度</strong></li></ul></li> <li>重写 <strong>update()</strong> 方法
<ul><li>判断 <strong>是否飞出屏幕</strong>，如果是，从 <strong>精灵组</strong> 删除</li></ul></li></ul> <h3 id="_2-1-敌机类的准备"><a href="#_2-1-敌机类的准备" class="header-anchor">#</a> 2.1 敌机类的准备</h3> <ul><li>在 <code>plane_sprites</code> 新建 <code>Enemy</code> 继承自 <code>GameSprite</code></li> <li>重写 <strong>初始化方法</strong>，直接指定 <strong>图片名称</strong></li> <li>暂时 <strong>不实现</strong> <strong>随机速度</strong> 和 <strong>随机位置</strong> 的指定</li> <li>重写 <code>update</code> 方法，判断是否飞出屏幕</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">class</span> <span class="token class-name">Enemy</span><span class="token punctuation">(</span>GameSprite<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token triple-quoted-string string">&quot;&quot;&quot;敌机精灵&quot;&quot;&quot;</span>
    
    <span class="token keyword">def</span> <span class="token function">__init__</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
        
        <span class="token comment"># 1. 调用父类方法，创建敌机精灵，并且指定敌机的图像</span>
        <span class="token builtin">super</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>__init__<span class="token punctuation">(</span><span class="token string">&quot;./images/enemy1.png&quot;</span><span class="token punctuation">)</span>

        <span class="token comment"># 2. 设置敌机的随机初始速度</span>

        <span class="token comment"># 3. 设置敌机的随机初始位置</span>
    
    <span class="token keyword">def</span> <span class="token function">update</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
        
        <span class="token comment"># 1. 调用父类方法，让敌机在垂直方向运动</span>
        <span class="token builtin">super</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>update<span class="token punctuation">(</span><span class="token punctuation">)</span>
        
        <span class="token comment"># 2. 判断是否飞出屏幕，如果是，需要将敌机从精灵组删除</span>
        <span class="token keyword">if</span> self<span class="token punctuation">.</span>rect<span class="token punctuation">.</span>y <span class="token operator">&gt;=</span> SCREEN_RECT<span class="token punctuation">.</span>height<span class="token punctuation">:</span>
            <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;敌机飞出屏幕...&quot;</span><span class="token punctuation">)</span>    
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br></div></div><h3 id="_2-2-创建敌机"><a href="#_2-2-创建敌机" class="header-anchor">#</a> 2.2 创建敌机</h3> <p><strong>演练步骤</strong></p> <ol><li>在 <code>__create_sprites</code>，添加 <strong>敌机精灵组</strong> <ul><li>敌机是 <strong>定时被创建的</strong>，因此在初始化方法中，不需要创建敌机</li></ul></li> <li>在 <code>__event_handler</code>，创建敌机，并且 <strong>添加到精灵组</strong> <ul><li>调用 <strong>精灵组</strong> 的 <code>add</code> 方法可以 <strong>向精灵组添加精灵</strong></li></ul></li> <li>在 <code>__update_sprites</code>，让 <strong>敌机精灵组</strong> 调用 <code>update</code> 和 <code>draw</code> 方法</li></ol> <p><img src="media/15025309517247/006_pygame.SpriteII.png" alt="006_pygame.SpriteII"></p> <p><strong>演练代码</strong></p> <ul><li>修改 <code>plane_main</code> 的 <code>__create_sprites</code> 方法</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 敌机组</span>
self<span class="token punctuation">.</span>enemy_group <span class="token operator">=</span> pygame<span class="token punctuation">.</span>sprite<span class="token punctuation">.</span>Group<span class="token punctuation">(</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><ul><li>修改 <code>plane_main</code> 的 <code>__update_sprites</code> 方法</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code>self<span class="token punctuation">.</span>enemy_group<span class="token punctuation">.</span>update<span class="token punctuation">(</span><span class="token punctuation">)</span>
self<span class="token punctuation">.</span>enemy_group<span class="token punctuation">.</span>draw<span class="token punctuation">(</span>self<span class="token punctuation">.</span>screen<span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><ul><li>定时出现敌机</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">elif</span> event<span class="token punctuation">.</span><span class="token builtin">type</span> <span class="token operator">==</span> CREATE_ENEMY_EVENT<span class="token punctuation">:</span>
    self<span class="token punctuation">.</span>enemy_group<span class="token punctuation">.</span>add<span class="token punctuation">(</span>Enemy<span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h3 id="_2-3-随机敌机位置和速度"><a href="#_2-3-随机敌机位置和速度" class="header-anchor">#</a> 2.3 随机敌机位置和速度</h3> <h4 id="_1-导入模块"><a href="#_1-导入模块" class="header-anchor">#</a> 1) 导入模块</h4> <ul><li>在导入模块时，<strong>建议</strong> 按照以下顺序导入</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token number">1.</span> 官方标准模块导入
<span class="token number">2.</span> 第三方模块导入
<span class="token number">3.</span> 应用程序模块导入
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br></div></div><ul><li>修改 <code>plane_sprites.py</code> 增加 <code>random</code> 的导入</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">import</span> random
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br></div></div><h4 id="_2-随机位置"><a href="#_2-随机位置" class="header-anchor">#</a> 2) 随机位置</h4> <p><img src="media/15025309517247/015_%E9%A3%9E%E6%9C%BA%E5%88%9D%E5%A7%8B%E4%BD%8D%E7%BD%AE.png" alt="015_飞机初始位置-w360"></p> <p>使用 <code>pygame.Rect</code> 提供的 <code>bottom</code> 属性，在指定敌机初始位置时，会比较方便</p> <ul><li><code>bottom = y + height</code></li> <li><code>y = bottom - height</code></li></ul> <h4 id="_3-代码实现"><a href="#_3-代码实现" class="header-anchor">#</a> 3) 代码实现</h4> <ul><li>修改 <strong>初始化方法</strong>，随机敌机出现 <strong>速度</strong> 和 <strong>位置</strong></li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">def</span> <span class="token function">__init__</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>

    <span class="token comment"># 1. 调用父类方法，创建敌机精灵，并且指定敌机的图像</span>
    <span class="token builtin">super</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>__init__<span class="token punctuation">(</span><span class="token string">&quot;./images/enemy1.png&quot;</span><span class="token punctuation">)</span>

    <span class="token comment"># 2. 设置敌机的随机初始速度 1 ~ 3</span>
    self<span class="token punctuation">.</span>speed <span class="token operator">=</span> random<span class="token punctuation">.</span>randint<span class="token punctuation">(</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">)</span>

    <span class="token comment"># 3. 设置敌机的随机初始位置</span>
    self<span class="token punctuation">.</span>rect<span class="token punctuation">.</span>bottom <span class="token operator">=</span> <span class="token number">0</span>
    
    max_x <span class="token operator">=</span> SCREEN_RECT<span class="token punctuation">.</span>width <span class="token operator">-</span> self<span class="token punctuation">.</span>rect<span class="token punctuation">.</span>width
    self<span class="token punctuation">.</span>rect<span class="token punctuation">.</span>x <span class="token operator">=</span> random<span class="token punctuation">.</span>randint<span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">,</span> max_x<span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br></div></div><h3 id="_2-4-移出屏幕销毁敌机"><a href="#_2-4-移出屏幕销毁敌机" class="header-anchor">#</a> 2.4 移出屏幕销毁敌机</h3> <ul><li>敌机移出屏幕之后，如果 <strong>没有撞到英雄</strong>，敌机的历史使命已经终结</li> <li>需要从 <strong>敌机组</strong> 删除，否则会造成 <strong>内存浪费</strong></li></ul> <h4 id="检测敌机被销毁"><a href="#检测敌机被销毁" class="header-anchor">#</a> 检测敌机被销毁</h4> <ul><li><code>__del__</code> 内置方法会在对象被销毁前调用，在开发中，可以用于 <strong>判断对象是否被销毁</strong></li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">def</span> <span class="token function">__del__</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;敌机挂了 %s&quot;</span> <span class="token operator">%</span> self<span class="token punctuation">.</span>rect<span class="token punctuation">)</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br></div></div><h4 id="代码实现"><a href="#代码实现" class="header-anchor">#</a> 代码实现</h4> <p><img src="media/15025309517247/006_pygame.SpriteII.png" alt="006_pygame.SpriteII"></p> <ul><li>判断敌机是否飞出屏幕，如果是，调用 <code>kill()</code> 方法从所有组中删除</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">def</span> <span class="token function">update</span><span class="token punctuation">(</span>self<span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token builtin">super</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span>update<span class="token punctuation">(</span><span class="token punctuation">)</span>
    
    <span class="token comment"># 判断敌机是否移出屏幕</span>
    <span class="token keyword">if</span> self<span class="token punctuation">.</span>rect<span class="token punctuation">.</span>y <span class="token operator">&gt;=</span> SCREEN_RECT<span class="token punctuation">.</span>height<span class="token punctuation">:</span>
        <span class="token comment"># 将精灵从所有组中删除</span>
        self<span class="token punctuation">.</span>kill<span class="token punctuation">(</span><span class="token punctuation">)</span>
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